<?php
echo "--> exchangeArray(array):\n";
$ao = new ArrayObject();
$ao->exchangeArray(array('original'));
var_dump($ao);

echo "\n--> exchangeArray(object):\n";
$obj = new stdClass;
$obj->newProp = 'changed';
$ao->exchangeArray($obj);
var_dump($ao);
?>

Actual output on PHP 5.3.0-dev (cli) (built: Jul 28 2008 00:21:59) :

--> exchangeArray(array):
object(ArrayObject)#1 (1) {
  ["storage":"ArrayObject":private]=>
  array(1) {
    [0]=>
    string(8) "original"
  }
}

--> exchangeArray(object):
object(ArrayObject)#1 (0) {
}